Liquid discharge apparatus

ABSTRACT

A liquid discharge apparatus includes first and second discharge sections, first and second connection paths and a voltage generation section. Each of the first and second discharge sections has a nozzle configured and arranged to discharge a liquid, a pressure chamber in communication with the nozzle, and a piezoelectric element. The first connection path selection section is arranged so as to correspond to the first discharge section and configured to selectively supply a plurality of voltages to the first discharge section. The second connection path selection section is arranged so as to correspond to the second discharge section and configured to selectively supply a plurality of voltages to the second discharge section. The voltage generation section is configured to generate and supply the voltages shared by the first connection path selection section and the second connection path selection section.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to Japanese Patent Application No.2013-059504 filed on Mar. 22, 2013. The entire disclosure of JapanesePatent Application No. 2013-059504 is hereby incorporated herein byreference.

BACKGROUND

1. Technical Field

The present invention relates to a feature for discharging droplets.

2. Related Art

A print apparatus for discharging droplets of ink from nozzles of aprint head by driving piezoelectric elements corresponding to each ofthe nozzles has been conventionally proposed. For example, JapaneseLaid-open Patent Publication No. 2013-006424 discloses a print apparatusin which a plurality of switches (transmission gates) corresponding at aone-to-one ratio to a plurality of piezoelectric elements are arranged,and shared control signals are selected for every piezoelectric elementby each of the switches and supplied to each of the piezoelectricelements.

SUMMARY

With a configuration in which shared control signals are selectivelysupplied to each of the piezoelectric elements, as in Japanese Laid-openPatent Publication No. 2013-006424, control signals of a very largeelectrical current must be supplied to the print head so that controlsignals of the proper waveform are supplied to each of the piezoelectricelements even in a case where a large number (for example, all) of thepiezoelectric elements are to be driven at the same time. As such, it isnecessary to fully ensure the withstand voltage performance andwithstand current performance of the circuitry used in the supply of thecontrol signals, and a problem arises in that it is difficult to reducethe scale of circuitry. In view of the above circumstances, an objectiveof the present invention is to reduce the withstand voltage performanceand withstand current performance that are required.

A liquid discharge apparatus according to one aspect includes first andsecond discharge sections, first and second connection paths and avoltage generation section. Each of the first and second dischargesections has a nozzle configured and arranged to discharge a liquid, apressure chamber in communication with the nozzle, and a piezoelectricelement provided for the pressure chamber and configured and arranged tocause the liquid to be discharged from the nozzle by charging anddischarging in accordance with a drive signal. The first connection pathselection section is configured to selectively supply a plurality ofvoltages to the first discharge section. The first connection pathselection section is arranged so as to correspond to the first dischargesection. The second connection path selection section is configured toselectively supply a plurality of voltages to the second dischargesection. The second connection path selection section is arranged so asto correspond to the second discharge section. The voltage generationsection is configured to generate and supply the voltages shared by thefirst connection path selection section and the second connection pathselection section. With the above configuration, the first connectionpath selection section corresponding to the first discharge section andthe second connection path selection section corresponding to the seconddischarge section are arranged, and the plurality of voltages suppliedfrom the voltage generation section are selectively supplied by thefirst connection path selection section to the first discharge sectionand selectively supplied by the second connection path selection sectionto the second discharge section. As such, an advantage arises in thatthe withstand voltage performance and withstand current performancerequired for the circuitry are reduced (and consequently the circuitryscale is reduced) in comparison to a configuration in which a controlsignal shared across a plurality of nozzles is individually selected byswitches of every nozzle and supplied to a piezoelectric element.

The liquid discharge apparatus as in the above aspect may furtherinclude a control signal supply section configured to supply a controlsignal, a first switch configured and arranged to controlsupply/shutting off of the control signal to the first connection pathselection section, and a second switch configured and arranged tocontrol supply/shutting off of the control signal to the secondconnection path selection section. The first connection path selectionsection may be configured to selectively supply the voltages to thefirst discharge section in accordance with the control signal suppliedfrom the first switch, and the second connection path selection sectionmay be configured to selectively supply the voltages to the seconddischarge section in accordance with the control signal supplied fromthe second switch. With the above configuration, a plurality of voltagesare selectively supplied to the piezoelectric elements in accordancewith the control signals supplied to each of the connection pathselection sections, by the control of the supply/shutting off of theshared control signal by each of the plurality of switches. As such, anadvantage arises in that the apparatus configuration and controlprocesses are simplified in comparison to a configuration in which thecontrol signal is individually generated for every discharge section.

The liquid discharge apparatus as in the above aspect may furtherinclude a first control signal supply section configured to generate acontrol signal and selectively supply the control signal to the firstconnection path selection section, the first control signal supplysection being arranged so as to correspond to the first connection pathselection section, and a second control signal supply section configuredto generate a control signal and selectively supply the control signalto the second connection path selection section, the second controlsignal supply section being arranged so as to correspond to the secondconnection path selection section. The first connection path selectionsection may be configured to selectively supply the voltages to thefirst discharge section in accordance with the control signal suppliedfrom the first control signal supply section, and the second connectionpath selection section may be configured to selectively supply thevoltages to the second discharge section in accordance with the controlsignal supplied from the second control signal supply section. With theabove aspect, the control signal supply sections installed for everydischarge section generate the control signals individually, andtherefore it is possible to adjust the control signal for everydischarge section, so that, for example, the differences in propertiesof each of the piezoelectric elements are compensated for.

The liquid discharge apparatus as in the above aspect may furtherinclude a first signal path through which a first voltage is applied bythe voltage generation section, and a second signal path through which asecond voltage higher than the first voltage is applied by the voltagegeneration section. The first connection path selection section mayelectrically connect the first discharge section and the voltagegeneration section by the first signal path or the second signal path inaccordance with a voltage of a control signal and a holding voltage ofthe piezoelectric element, and the second connection path selectionsection may electrically connect the second discharge section and thevoltage generation section by the first signal path or the second signalpath in accordance with the voltage of the control signal and theholding voltage of the piezoelectric element. With the above aspect,charging or discharging of the piezoelectric element is executed byelectrically connecting the piezoelectric element to the first signalpath or the second signal path; also, this electrical connection isdefined taking not only the voltage of the control signal into accountbut also the holding voltage of the piezoelectric element. Therefore,the piezoelectric element can be finely controlled. Also, the chargingand discharging of the piezoelectric element proceeds in a stepwisemanner, and therefore the energy efficiency can be increased compared toa conventional configuration where charging and discharging areperformed all at once between power source voltages. The occurrence ofelectromagnetic interference (EMI) can also be minimized, because alarge current is not switched, as in class D amplification.

A liquid discharge apparatus as in a preferred aspect of the presentinvention is equipped with a detection section for detecting whether ornot the holding voltage of the piezoelectric element is less than thefirst voltage, or whether or not the holding voltage of thepiezoelectric is between the first voltage and less than the secondvoltage. With the above aspect, whether or not the holding voltage ofthe piezoelectric element is less than the first voltage, or whether ornot the holding voltage of the piezoelectric is between the firstvoltage and less than the second voltage, is detected. As the detectionsection, a portion for detecting whether or not the holding voltage ofthe piezoelectric element is less than the first voltage and a portionfor detecting whether or not the holding voltage of the piezoelectricelement is between the first voltage and less than second voltage may beindividually divided or may be integrated together.

In another aspect, each of a plurality of connection path selectionsections comprising the first connection path selection section and thesecond connection path selection section control a charge with which thepiezoelectric element is charged via the first signal path in conformitywith the voltage of the control signal at less than the first voltage,and control a charge discharged from the piezoelectric element via thefirst signal path or a charge with which the piezoelectric element ischarged via the second signal path in accordance with the voltage of thecontrol signal at between the first voltage and less than the secondvoltage. According to the above aspect, the charge by which thepiezoelectric element is charged/discharged is controlled in conformitywith the voltage of the control signal.

In another aspect, each of the plurality of connection path selectionsections comprises a first transistor, a second transistor, and a thirdtransistor, wherein at less than the first voltage, the first transistorcontrols a charge with which the piezoelectric element is charged viathe first signal path in accordance with a voltage obtained when thevoltage of the control signal is shifted by a predetermined value to alow side, and at between the first voltage and less than the secondvoltage, the second transistor controls a charge discharged from thepiezoelectric element via the first signal path in accordance with avoltage obtained when the voltage of the control signal is shifted bythe predetermined value to a high side, and the third transistorcontrols a charge with which the piezoelectric element is charged viathe second signal path in accordance with a voltage obtained when thevoltage of the control signal is shifted by the predetermined value tothe low side. In the above aspect, preferably, the predetermined valueshould be zero when the first transistor, the second transistor, and thethird transistor are ideal, but, for example, is a voltage equivalent toa bypass voltage with a bipolar transistor or, for example, a voltageequivalent to a threshold value voltage with a metal-oxide semiconductorfield effect transistor (MOSFET).

In another aspect, the first transistor is off at not less than thefirst voltage, and the second transistor and the third transistor areoff at not between the first voltage and less than the second voltage.The above aspect causes the first transistor to be off, and thereforecauses the piezoelectric element to be electrically disconnected fromthe first signal path, when the holding voltage of the piezoelectricelement is not less than the first voltage; and also causes the secondtransistor and the third transistor to be off, and therefore causes thepiezoelectric element to be electrically disconnected from the secondsignal path, when the holding voltage of the piezoelectric element isnot between the first voltage and less than the second voltage.

In another aspect, each of the plurality of connection path selectionsections controls charge with which the piezoelectric element is chargedor the charge discharged from the piezoelectric element, at a voltageobtained when a voltage found by subtracting a voltage held by thepiezoelectric element from the voltage of the control signal ismultiplied by a predetermined number. According to the above aspect, anegative feedback control makes it possible to cause the voltage held inthe piezoelectric element to track the voltage of an input signal withhigh accuracy and in a short time.

BRIEF DESCRIPTION OF THE DRAWINGS

Referring now to the attached drawings which form a part of thisoriginal disclosure:

FIG. 1 is a drawing illustrating a schematic configuration of a printapparatus;

FIG. 2 is a drawing for describing a control signal;

FIG. 3 is a drawing illustrating the principal configuration of adischarge section in a print head;

FIG. 4 is a partial block diagram of a print head;

FIG. 5 is a drawing illustrating one example of the configuration of adriver in a print head;

FIGS. 6A and 6B are diagrams for describing the operation of a driver;

FIGS. 7A to 7C are drawings for describing the operation of a levelshifter in a driver;

FIG. 8 is a drawing for describing the flow of an electrical current(charge) in a driver;

FIG. 9 is a drawing for describing the flow of an electrical current(charge) in a driver;

FIG. 10 is a drawing for describing the flow of an electrical current(charge) in a driver;

FIG. 11 is a drawing for describing the flow of an electrical current(charge) in a driver;

FIGS. 12A and 12B are drawings for describing loss during charging anddischarging of a driver;

FIG. 13 is a drawing illustrating one example of the configuration of anauxiliary power source circuit;

FIGS. 14A and 14B are drawings for describing the operation of anauxiliary power source circuit;

FIG. 15 is a drawing illustrating the schematic configuration of a printapparatus in a second embodiment;

FIG. 16 is a drawing illustrating one example of the configuration of a(first) example of application of a driver; and

FIG. 17 is a drawing illustrating one example of the configuration of a(second) example of application of a driver.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS First Embodiment

FIG. 1 is a block diagram of a print apparatus 100A as in a firstembodiment of the present invention. The print apparatus 100A of thefirst embodiment is a liquid discharge for printing an image on arecording medium such as print paper by discharging droplets of ink(“ink droplets”) onto the recording medium.

As illustrated in FIG. 1, the print apparatus 100A is equipped with acontrol unit 10, a print head 20, and a flexible flat cable (FFC) 70.The ink droplets are discharged onto the recording medium from each of aplurality of nozzles of the print head 20, on the basis of a control bythe control unit 10. The print apparatus 100A of the first embodiment isa serial-type inkjet printer in which the print head 20 is mounted ontoa carriage (not shown) for moving in a direction (main scanningdirection) that intersects with a direction of conveyance (secondaryscanning direction) of the recording medium. The control unit 10 isarranged on a control substrate (not shown) outside of the carriage. TheFFC 70 is a flexible wiring substrate for electrically connecting thecontrol unit 10 and the print head 20.

The control unit 10 is an element for executing a computational processand control process for printing an image that has been designated withimage data supplied from a host computer (not shown), and is equippedwith a print data generation section 120, a control signal supplysection 140, and a main power source section 180.

The main power source section 180 generates a power source voltage V_(H)and a ground potential (grounding) G. The ground G is equivalent to areference value for voltage (voltage zero), and the power source voltageV_(H) is a voltage on a high side of the ground G. The power sourcevoltage V_(H) and the ground G are supplied to the print head 20 via theFFC 70.

The print data generation section 120 and the control signal supplysection 140 in FIG. 1 are implemented by, for example, a computationalprocessing device (central processing unit (CPU)) and a variety of logiccircuits for executing programs stored in a storage circuit such as aRAM. An element for controlling a conveyance mechanism for conveying therecording medium and an element for controlling a movement mechanism formoving the carriage are also installed in the control unit 10, but FIG.1 omits depictions thereof for the sake of convenience.

The print data generation section 120 generates print data DP byexecuting a variety of computational processes (for example, an imagedevelopment process, color conversion process, color separation process,halftone process, and the like) on the image data that is supplied fromthe host computer. The print data DP specifies, for every nozzle of theprint head 20, whether or not ink droplets are to be discharged, and theamount of ink droplets discharged. The print data DP generated by theprint data generation section 120 is supplied to the print head 20 viathe FFC 70.

The control signal supply section 140 generates control signals COM(COMA, COMB) for causing the ink droplets to be discharged from each ofthe nozzles of the print head 20. The control signal supply section 140of the first embodiment is configured so as to comprise a firstgeneration section 141 for generating the control signal COMA and asecond generation section 142 for generating the control signal COMB.Each of the first generation section 141 and the second generationsection 142 is equipped with a waveform generation section 144 forgenerating a digital control signal dCOM and a D/A converter 145 forconverting the control signal dCOM into the analog control signals COM(COMA, COMB). As is illustratively exemplified in FIG. 2, each of thecontrol signal COMA and the control signal COMB is a voltage signal inwhich a plurality of drive pulses are arranged in time series in everyprint cycle (one cycle) Ta. The control signal COMA and the controlsignal COMB have different waveforms. It would also be possible toemploy a configuration in which only the one system of the controlsignal COM is supplied to the print head 20 from the control unit 10, ora configuration in which the control signal COMA and the control signalCOMB are each supplied to the print head 20 from the control unit 10 asdifferential signals.

As illustrated in FIG. 1, the print head 20 is equipped with a headcontrol section 220, a selection section 230, an element drive section240, an auxiliary power source section 50, and a piezoelectric elementgroup 260. The piezoelectric element group 260 is equipped with aplurality of piezoelectric elements 40 that correspond to differentnozzles. Each of the piezoelectric elements 40 is a capacitive load thatis arranged in a cavity (ink chamber) to which ink is supplied via aflow path. Charging and discharging by the supply of voltages causes thepiezoelectric elements 40 to deform and the volume of the cavity tovary, as a result of which the ink droplets are discharged from thenozzles corresponding to the piezoelectric elements 40.

FIG. 3 is a drawing illustrating the schematic configuration of adischarge section 400 corresponding to one nozzle worth of the printhead 20. As illustrated in FIG. 3, the discharge section 400 comprises apiezoelectric element 40, a diaphragm 421, a cavity (pressure chamber)431, a reservoir 441, and a nozzle 451. Of these, the diaphragm 421 isdeformed by the piezoelectric element 40, which is provided to an uppersurface in FIG. 3, and expands or reduces the internal volume of thecavity 431, which is filled with ink. The nozzle 451 is an opening thatcommunicates with the cavity 431.

The piezoelectric element 40 illustrated in FIG. 3 is typically astructure called a unimorph (monomorph) type, in which a piezoelectricbody 401 is interposed between a pair of electrodes 411, 412. In thepiezoelectric body 401 of this structure, a middle portion in FIG. 3 iswarped in the vertical direction, with respect to both end portions,along with the electrodes 411, 412 and the diaphragm 421 in accordancewith a voltage applied between the electrodes 411, 412. Here, in upwardwarping, the internal volume of the cavity 431 is expanded, and thus theink is drawn in from the reservoir 441, whereas with downward warping,the internal volume of the cavity 431 is expanded, and thus the ink isdischarged from the nozzle 451. The piezoelectric element 40 is notlimited to being the unimorph type, however, and need only be a type,such as a bimorph type or laminated type, with which the piezoelectricelement can be deformed to discharge a liquid such as ink.

The element drive section 240 is an element for driving each of theplurality of piezoelectric elements 40, and is configured so as tocomprise a plurality (the same number as that of the piezoelectricelements 40) of drivers 30 corresponding to the different piezoelectricelements 40 of the piezoelectric element group 260, as illustrated inFIG. 1. That is to say, each of the drivers 30 of the element drivesection 240 and each of the piezoelectric elements 40 of thepiezoelectric element group 260 have a one-to-one correspondence, andthe print head 20 comprises a plurality of the sets of the piezoelectricelements 40 and the drivers 30. One end of each of the piezoelectricelements 40 is connected to an output end of the driver 30 correspondingto the relevant piezoelectric element 40, and the other end of each ofthe piezoelectric elements 40 is grounded to the ground G.

The selection section 230 is equipped with a plurality (the same numberas that of the piezoelectric elements 40) of switches 232 correspondingto the different piezoelectric elements 40. Each of the switches 232 isin one-to-one correspondence with each of the sets of the drivers 30 andthe piezoelectric elements 40. Supplied in common to an input end ofeach of the switches 232 of the selection section 230 are the controlsignal COMA and the control signal COMB generated by the control signalsupply section 140, and an output end of each of the switches 232 isconnected to the input end of the driver 30 corresponding to therelevant switch 232. Each of the switches 232 selects either the controlsignal COMA or the control signal COMB and supplies same to the driver30.

The head control section 220 of FIG. 1 controls each of the plurality ofswitches 232 of the selection section 230 in accordance with the printdata DP that is supplied from the print data generation section 120.More specifically, the head control section 220 selects either thecontrol signal COMA or the control signal COMB for each of the switches232 in each of a plurality of segments t obtained when the print cycleTa of the control signal COMA and the control signal COMB is divided onthe time axis, as illustrated in FIG. 2. As such, a control signal Vin,obtained when either the control signal COMA or the control signal COMBis selectively extracted for every segment t, is supplied from theswitches 232 to the drivers 30 of the subsequent stage.

The auxiliary power source section 50 of FIG. 1 is a voltage generationsection (step-up circuit) for utilizing the voltage V_(H) supplied fromthe main power source section 180 of the control unit 10 to generate aplurality of voltages. The auxiliary power source section 50 of thefirst embodiment uses a charge pump circuit to divide and redistributethe voltage V_(H), thereby generating a voltage (V_(H)/6) that is afactor of ⅙ of the relevant voltage V_(H), a voltage (2V_(H)/6) that isa factor of 2/6 thereof, a voltage (3V_(H)/6) that is a factor of 3/6thereof, a voltage (4V_(H)/6) that is a factor of 4/6 thereof, and avoltage (5V_(H)/6) that is a factor of ⅚ thereof, as is illustrated inFIG. 4. The plurality of voltages generated by the auxiliary powersource section 50 are supplied in common to the plurality of drivers 30of the element drive section 240. That is to say, the plurality ofdrivers 30 share the auxiliary power source section 50. Each of thedrivers 30 is a circuit (connection path selection section) forutilizing the plurality of voltages supplied from the auxiliary powersource section 50 to drive the piezoelectric elements in accordance withthe control signal Vin supplied from the selection section 230. Morespecifically, a voltage Vout that varies tracking the voltage of thecontrol signal Vin is supplied to the piezoelectric elements 40 fromeach of the drivers 30. Because one end of the piezoelectric elements 40is grounded, the voltage Vout is equivalent to a voltage held by thepiezoelectric elements 40.

Driver

FIG. 5 is a drawing illustrating one example of the configuration of thedriver 30 for driving one piezoelectric element 40 in the firstembodiment. As illustrated in FIG. 5, including voltage zero, the driver30 utilizes seven types of voltage—more specifically, voltage zero(ground G), V_(H)/6, 2V_(H)/6, 3V_(H)/6, 4V_(H)/6, 5V_(H)/6, V_(H), inascending—to generate the voltage Vout. The voltage V_(H)/6 is suppliedto the driver 30 from the auxiliary power source section 50 via a powersource wiring 511 and, similarly, the voltages 2V_(H)/6, 3V_(H)/6,4V_(H)/6, 5V_(H)/6 are supplied to each of the drivers 30 from theauxiliary power source section 50 via power source wirings 512, 513,514, 515. As illustrated in FIG. 5, the driver 30 comprises anoperational amplifier 30, unit circuits 34 a to 34 f, and comparators 38a to 38 e, and drives the piezoelectric element 40 in conformity withthe control signal Vin.

The control signals Vin, which are outputted from the selection section230, are supplied to an input end (+) of the operational amplifier 32,which is an input end of the driver 30. Output signals of theoperational amplifier 32 are supplied to the unit circuits 34 a to 34 f,negatively fed back to an input end (−) of the operational amplifier 32via a resistor Rf, and also grounded to the ground G via a resistor Rin.For this reason, the operational amplifier 32 non-invertingly amplifiesthe control signals Vin by a factor of (1+Rf/Rin).

The voltage amplification factor of the operational amplifier 32 can beset by the resistors Rf, Rin, but for the sake of convenience, Rf isunderstood to be zero and Rin is understood to be infinite below. Thatis to say, the following description understands the voltageamplification factor of the operational amplifier 32 to have been set to“1” and understands the control signals Vin to be supplied to the unitcircuits 34 a to 34 f without alteration. The voltage amplificationfactor may be a number other than “1”.

The unit circuits 34 a to 34 f are provided in ascending order ofvoltage so as to correspond to two mutually adjacent voltages out of theaforementioned types of voltages. More specifically, the unit circuit 34a is provided so as to correspond to voltage zero and the voltageV_(H)/6, the unit circuit 34 b is provided so as to correspond to thevoltage V_(H)/6 and the voltage 2V_(H) 6, the unit circuit 34 c isprovided so as to correspond to the voltage 2V_(H)/6 and the voltage3V_(H)/6, the unit circuit 34 d is provided so as to correspond to thevoltage 3V_(H)/6 and the voltage 4V_(H)/6, the unit circuit 34 e isprovided so as to correspond to the voltage 4V_(H)/6 and the voltage5V_(H)/6, and the unit circuit 34 f is provided so as to correspond tothe voltage 5V_(H)/6 and the voltage V_(H).

The circuitry configurations of the unit circuits 34 a to 34 f aremutually identical, and comprise whichever one respectively correspondsout of level shifters 36 a to 36 f, a bipolar NPN transistor 341, and aPNP transistor 342.

Where the unit circuits 34 a to 34 f are described in general ratherthan specific terms, then the description shall simply relate to areference numeral “34”; likewise, where the level shifters 36 a to 36 fare described in general rather than specific terms, then thedescription shall simply relate to a reference numeral “36”.

The level shifters 36 take either an enable state or a disable state.More specifically, the level shifters 36 are in the enable state whenthe signal supplied to a negative control end, marked with a circle, isan L level and the signal supplied to a positive control end, not markedwith a circle, is an H level; at all other times, the level shifters 36are in the disable state.

As will be described below, out of the aforementioned seven types ofvoltages, each of the comparators 38 a to 38 e is associated by pairswith five types of voltages, excluding voltage zero and the voltageV_(H). Focusing herein on a given unit circuit 34, the output signal ofthe comparator associated with a high-side voltage out of the twovoltages associated with the relevant unit circuit 34 is supplied to thenegative control end of the level shifter 36 in the relevant unitcircuit 34, and the output signal of the comparator associated with alow-side voltage out of the two voltages associated with the relevantunit circuit is supplied to the positive control end of the levelshifter 36. The negative control end of the level shifter 36 f in theunit circuit 34 f is grounded to the ground G of voltage zero,equivalent to the L level, and the positive control end of the levelshifter 36 a in the unit circuit 34 a is connected to the power sourcewiring 516, which supplies the voltage V_(H), equivalent to the H level.

The level shifters 36, when in the enable state, shift the voltage ofthe inputted control signals Vin by a predetermined value in a minusdirection and supply the shifted voltage to a base terminal of thetransistors 341, and in turn shift the voltage of the control signalsVin by a predetermined value in a plus direction and supply the shiftedvoltage to a base terminal of the transistor 342. Irrespective of thecontrol signals Vin, the level shifters 36 when in the disable statesupply a voltage for turning the transistors 341 off, e.g., the voltageV_(H) to the base terminals of the relevant transistors 341, and supplya voltage for turning the transistors 342 off, e.g., voltage zero to thebase terminals of the relevant transistors 342.

The predetermined value is understood to be a voltage (bias voltage,about 0.6 V) between a base and emitter, at which a current begins toflow to an emitter terminal. For this reason, the predetermined value isa quality determined in accordance with the properties of thetransistors 341, 342, and is zero provided that the transistors 341, 342are ideal.

A collector terminal of the transistor 341 is connected to the powersource wiring that supplies the high-side voltage out of the twocorresponding voltages, and a collector terminal of the transistor 342is connected to the power source wiring that supplies the low-sidevoltage. In, for example, the unit circuit 34 a, which corresponds tovoltage zero and the voltage V_(H)/6, the collector terminal of thetransistor 341 is connected to the power source wiring 511, whichsupplies the voltage V_(H)/6, and the collector terminal of thetransistor 342 is grounded to the ground G of voltage zero. In anotherexample, in the unit circuit 34 b, which corresponds to the voltageV_(H)/6 and the voltage 2V_(H)/6, the collector terminal of thetransistor 341 is connected to the power source wiring 512, whichsupplies the voltage 2V_(H)/6, and the collector terminal of thetransistor 342 is connected to the power source wiring 511, whichsupplies the voltage V_(H)/6. In the unit circuit 34 f, whichcorresponds to the voltage 5V_(H)/6 and the voltage V_(H), the collectorterminal of the transistor 341 is connected to the power source wiring516, which supplies the voltage V_(H), and the collector terminal of thetransistor 342 is connected to the power source wiring 515, whichsupplies the voltage 5V_(H)/6.

In turn, in the unit circuits 34 a to 34 f, emitter terminals of thetransistors 341, 342 share a connection to one end of the piezoelectricelement 40. For this reason, the common connection point of the emitterterminals of the transistors 341, 342 is connected to the one end of thepiezoelectric element 40 as an output end of the driver 30.

Out of the aforementioned seven types of voltages, the comparators 38 ato 38 e correspond to five types of voltages V_(H)/6, 2V_(H)/6,3V_(H)/6, 4V_(H)/6, 5V_(H)/6, V_(H), excluding voltage zero and thevoltage V_(H), and compare the relative levels of voltages supplied tothe two input ends and output a signal indicative of the comparisonresult. Herein, out of the two input ends in the comparators 38 a to 38e, one end is connected to the power source wiring that supplies thevoltage that corresponds thereto, and the other end shares a connectionto the one end of the piezoelectric element 40, along with each of theemitter terminals of the transistors 341, 342. For example, in thecomparator 38 a, which corresponds to the voltage V_(H)/6, one end outof the two input ends is connected to the power source wiring 511, whichsupplies the voltage V_(H)/6 corresponding thereto; in another example,in the comparator 38 b, which corresponds to the voltage 2V_(H)/6, oneend of the two input ends is connected to the power source wiring 512,which supplies the voltage 2V_(H)/6 corresponding thereto.

Each of the comparators 38 a to 38 e outputs a signal which takes the Hlevel when the voltage Vout of the other end at the input end is notless than the voltage of the one end, and takes the L level when thevoltage Vout is less than the voltage of the one end.

More specifically, for example, the comparator 38 a outputs a signalwhich takes the H level when the voltage Vout is not less than thevoltage V_(H)/6, and takes the L level when the voltage Vout is lessthan the voltage V_(H)/6. As another example, the comparator 38 boutputs a signal which takes the H level when the voltage Vout is notless than the voltage 2V_(H)/6, and takes the L level when the voltageVout is less than the voltage 2V_(H)/6.

To focus now on one out of the five types of voltages, the output signalof the comparator corresponding to the relevant voltage of interest issupplied to both the negative input end of the level shifter 36 of theunit circuit for which the relevant voltage is the high-side voltage,and the positive input end of the level shifter 36 of the unit circuitfor which the relevant voltage is the low-side voltage.

For example, the output signal of the comparator 38 a, which correspondsto the voltage V_(H)/6, is supplied to the negative input end of thelevel shifter 36 a of the unit circuit 34 a, for which the relevantvoltage V_(H)/6 is associated as the high-sigh voltage, and to thepositive input end of the level shifter 36 b of the unit circuit 34 b,for which the relevant voltage V_(H)/6 is associated as the low-sidevoltage. As another example, the output signal of the comparator 38 b,which corresponds to the voltage 2V_(H)/6, is supplied to the negativeinput end of the level shifter 36 b of the unit circuit 34 b, for whichthe relevant voltage 2V_(H)/6 is associated as the high-sigh voltage,and to the positive input end of the level shifter 36 c of the unitcircuit 34 c, for which the relevant voltage 2V_(H)/6 is associated asthe low-side voltage.

Next, the operation of the driver 30 shall now be described.

First, the states reached by the comparators 38 a to 38 e and the levelshifters 36 with respect to the voltage Vout, held by the piezoelectricelement 40, shall be described.

In a state (first state) where the voltage Vout is between voltage zeroand less than the voltage V_(H)/6, then the output signals of thecomparators 38 a to 38 e are all at the L level. For this reason, in thefirst state, only the level shifter 36 a is in the enable state, and theother level shifters 36 b to 36 f are in the disable state.

In a state (second state) where the voltage Vout is not less than thevoltage V_(H)/6 but is less than the voltage 2V_(H)/6, then the outputsignal of the comparator 38 a is at the H level, and the output signalsof the other comparators 38 b to 38 e are at the L level. For thisreason, in the second state, only the level shifter 36 b is in theenable state, and the other level shifters 36 a, 36 c to 36 f are in thedisable state.

In a state (third state) where the voltage Vout is not less than thevoltage 2V_(H)/6 but is less than the voltage 3V_(H)/6, then the outputsignals of the comparators 38 a, 38 b are at the H level, and the outputsignals of the other comparators 38 c to 38 e are at the L level. Forthis reason, in the third state, only the level shifter 36 c is in theenable state, and the other level shifters 36 a, 36 b, 36 d to 36 f arein the disable state.

In a state (fourth state) where the voltage Vout is not less than thevoltage 3V_(H)/6 but is less than the voltage 4V_(H)/6, then the outputsignals of the comparators 38 a, 38 b, 38 c are at the H level, and theoutput signals of the other comparators 38 d to 38 e are at the L level.For this reason, in the fourth state, only the level shifter 36 d is inthe enable state, and the other level shifters 36 a to 36 c, 36 e, 36 fare in the disable state.

In a state (fifth state) where the voltage Vout is not less than thevoltage 4V_(H)/6 but is less than the voltage 5V_(H)/6, then the outputsignals of the comparators 38 a to 38 d are at the H level, and theoutput signal of the other comparator 38 e is at the L level. For thisreason, in the fifth state, only the level shifter 36 e is in the enablestate, and the other level shifters 36 a to 36 d, 36 f are in thedisable state.

In a state (sixth state) where the voltage Vout is not less than thevoltage 5V_(H)/6 but is less than the voltage V_(H), then the outputsignals of the comparators 38 a to 38 e are all at the H level. For thisreason, in the sixth state, only the level shifter 36 f is in the enablestate, and the other level shifters 36 a to 36 d are in the disablestate.

Thus, in the first state, only the level shifter 36 a is in the enablestate. This continues in a similar manner, where only the level shifter36 b is in the enable state in the second state, only the level shifter36 c is in the enable state in the third state, only the level shifter36 d is in the enable state in the fourth state, only the level shifter36 e is in the enable state in the fifth state, and only the levelshifter 36 f is in the enable state in the sixth state.

The first state through sixth state have been defined with the voltageVout, but this could also be stated in terms of the state of charge held(stored) in the piezoelectric element 40.

When the level shifter 36 a is in the enable state in the first state,then the relevant level shifter 36 a supplies a voltage signal obtainedwhen the control signal Vin has been level-shifted by a predeterminedvalue in the minus direction to the base terminal of the transistor 341in the unit circuit 34 a, and supplies a voltage signal obtained whenthe control signal Vin has been level-shifted by a predetermined valuein the plus direction to the base terminal of the transistor 342 in therelevant unit circuit 34 a.

Herein, when the voltage of the control signal Vin is higher than thevoltage Vout (connection point voltage between the emitter terminals),then a current corresponding to the difference thereof (the voltagebetween base and emitter; in a stricter sense, a voltage reduced by apredetermined value from the voltage between base and emitter) flows tothe emitter terminal from the collector terminal of the transistor 341.For this reason, the voltage Vout gradually rises and approaches thevoltage of the control signal Vin, and when the voltage Vout eventuallymatches the voltage of the control signal Vin, then the current flowingto the transistor 341 at this point in time is zero.

In turn, when the voltage of the control signal Vin is less than thevoltage Vout, then a current corresponding to the difference flows tothe collector terminal from the emitter terminal of the transistor 342.For this reason, the voltage Vout gradually lowers and approaches thevoltage of the control signal Vin, and when the voltage Vout eventuallymatches the voltage of the control signal Vin, then the current flowingto the transistor 342 at this point in time is zero.

As such, in the first state, the transistors 341, 342 of the unitcircuit 34 a will execute such a control as to match the voltage Vout tothe control signal Vin.

In the first state, because the level shifters 36 are in the disablestate in the unit circuits 34 b to 34 f other than the unit circuit 34a, the voltage V_(H) is supplied to the base terminals of thetransistors 341, and voltage zero is supplied to the base terminals ofthe transistors 342. For this reason, in the first state, thetransistors 341, 341 are off in the unit circuits 34 b to 34 f, andtherefore are not involved in the control of the voltage Vout.

The description herein is of when the first state is in effect, but theoperation will be similar in the second state through sixth state, aswell. More specifically, one of the unit circuits 34 a to 34 f isenabled, depending on the voltage Vout held by the piezoelectric element40, and the transistors 341, 342 of the enabled unit circuit implement acontrol so as to match the voltage Vout to the control signal Vin. Forthis reason, when the driver 30 is viewed as a whole, the operation isone where the voltage Vout tracks the voltage of the control signal Vin.

As such, as illustrated in FIG. 6A, when the control signal Vin rises,for example, from voltage zero to the voltage V_(H), then the voltageVout also tracks the control signal Vin and changes from voltage zero tothe voltage V_(H). As illustrated in FIG. 6B, when the control signalVin lowers from the voltage V_(H) to voltage zero, then the voltage Voutalso tracks the control signal Vin and changes from the voltage V_(H) tovoltage zero.

FIGS. 7A to 7C are drawings for describing the operation of the levelshifters.

When the voltage of the control signal Vin changes, rising from voltagezero to the voltage V_(H), the voltage Vout also tracks the controlsignal Vin and rises. In the course of this rise, the level shifter 36 ais in the enable state when the first state, where the voltage Vout isbetween voltage zero and less than the voltage V_(H)/6, is in effect.For this reason, as illustrated in FIG. 7A, the voltage (denoted by“P-type”) that is supplied to the base terminal of the transistor 341 bythe level shifter 36 a is a voltage obtained when the control signal Vinhas been shifted by a predetermined value in the minus direction, andthe voltage (denoted by “N-type”) that is supplied to the base terminalof the transistor 342 is a voltage obtained when the control signal Vinhas been shifted by a predetermined value in the plus direction. When astate other than the first state is in effect, however, then the levelshifter 36 a is in the disable state, and therefore the voltage that issupplied to the base terminal of the transistor 341 is V_(H), and thevoltage that is supplied to the base terminal of the transistor 342 iszero.

FIG. 7B illustrates a voltage waveform outputted by the level shifter 36b, and FIG. 7C illustrates a voltage waveform outputted by the levelshifter 36 f. No special description shall be needed provided that oneremembers that the level shifter 36 b is in the enable state when thesecond state, where the voltage Vout is between the voltage 2V_(H)/6 andless than the voltage 2V_(H)/6, is in effect, and that the level shifter36 f is in the enable state when the sixth state, where the voltage Voutis between the voltage 5V_(H)/6 and less than the voltage V_(H), is ineffect.

The description shall also forgo describing the operation of the levelshifters 36 c to 36 e in the course of rising of the voltage of thecontrol signal Vin (or the voltage Vout), and describing the operationof the level shifters 36 a to 36 f in the course of lowering of thevoltage of the control signal Vin (or the voltage Vout).

Next, the flow of current (charge) in the unit circuits 34 a to 34 fshall be described, taking the unit circuits 34 a, 34 b by way ofexample, and divided between during charging and during discharging.

FIG. 8 is a drawing illustrating the operation of when the piezoelectricelement 40 is charged when the first state (a state where the voltageVout is between voltage zero and less than the voltage V_(H)/6) is ineffect.

In the first state, the level shifter 36 a is in the enable state andthe other level shifters 36 b to 36 f are in the disable state, andtherefore it suffices to focus only on the unit circuit 34 a.

When the voltage of the control signal Vin is higher than the voltageVout in the first state, then a current corresponding to the voltagebetween base and emitter flows through the transistor 341 of the unitcircuit 34 a. As such, the transistor 341 of the unit circuit 34 a willfunction as a first transistor. At this time, the transistor 342 of theunit circuit 34 a is off.

At this time, the electrical current flows in a path that goes from thepower source wiring 511→the transistor 341 (of the unit circuit 34a)→the piezoelectric element 40, as illustrated by the arrow in FIG. 8,thus charging the piezoelectric element 40 with a charge. This chargingcauses the voltage Vout to rise.

When the voltage Vout matches the voltage of the control signal Vin, thetransistor 341 of the unit circuit 34 a is off, and therefore thecharging of the piezoelectric element 40 is stopped.

However, in a case where the control signal Vin rises to the voltageV_(H)/6 or higher, then the voltage Vout also tracks the control signalVin and therefore reaches the voltage V_(H)/6 or higher as well, and atransition is made from the first state to the second state (a statewhere the voltage Vout is between the voltage V_(H)/6 and less than thevoltage 2V_(H)/6).

FIG. 9 is a drawing illustrating the operation of when the piezoelectricelement 40 is charged in the second state.

In the second state, the level shifter 36 b is in the enable state andthe other level shifters 36 a, 36 c to 36 f are in the disable state,and therefore it suffices to focus only on the unit circuit 34 b.

When the voltage of the control signal Vin is higher than the voltageVout in the second state, then a current corresponding to the voltagebetween base and emitter flows through the transistor 341 of the unitcircuit 34 b. As such, the transistor 341 of the unit circuit 34 b willfunction as a third transistor. At this time, the transistor 342 of theunit circuit 34 b is off.

At this time, the electrical current flows in a path that goes from thepower source wiring 512→the transistor 341 (of the unit circuit 34b)→the piezoelectric element 40, as illustrated by the arrow in FIG. 9,thus charging the piezoelectric element 40 with a charge. That is tosay, in a case where the piezoelectric element 40 is charged in thesecond state, one end of the piezoelectric element 40 is electricallyconnected to the auxiliary power source section 50 via the power sourcewiring 512.

Thus, when a transition is made from the first state to the second stateduring rising of the voltage Vout, then the source of supply of theelectric current is switched from the power source wiring 511 to thepower source wiring 512.

When the voltage Vout matches the voltage of the control signal Vin, thetransistor 341 of the unit circuit 34 b is off, and therefore thecharging of the piezoelectric element 40 is stopped.

However, in a case where the control signal Vin rises to the voltage2V_(H)/6 or higher, then the voltage Vout also tracks the control signalVin and therefore reaches the voltage 2V_(H)/6 or higher as well, as aresult of which a transition is made from the second state to the thirdstate (a state where the voltage Vout is between the voltage 2V_(H)/6and less than the voltage 3V_(H)/6).

In the charging operation from the third state to the sixth state,though not shown, the source of supply of the electrical current isswitched in a stepwise manner to the power source wirings 513, 514, 515,516.

FIG. 10 is a drawing illustrating the operation of when thepiezoelectric element 40 is discharged when the second state is ineffect.

In the second state, the level shifter 36 b is in the enable state. Whenthe voltage of the control signal Vin is lower than the voltage Vout inthis state, then a current corresponding to the voltage between base andemitter flows through the transistor 342 of the unit circuit 34 b. Assuch, the transistor 341 of the unit circuit 34 b will function as asecond transistor. At this time, the transistor 341 of the unit circuit34 b is off.

At this time, the electrical current flows in a path that goes from thepiezoelectric element 40→the transistor 342 (of the unit circuit 34b)→the power source wiring 511, as illustrated by the arrow in FIG. 10,thus discharging the charge from the piezoelectric element 40. That isto say, in a case where the piezoelectric element 40 is charged with acharge in the first state, and in a case where a charge is dischargedfrom the piezoelectric element 40 in the second state, then one end ofthe piezoelectric element 40 is electrically connected to the auxiliarypower source section 50 via the power source wiring 511. Further, thepower source wiring 511 supplies a current (charge) during charging inthe first state, and recovers a current (charge) during discharging ofthe second state.

The recovered charge is redistributed for reuse by the auxiliary powersource section 50 (described below).

When the voltage Vout matches the control signal Vin, the transistor 342of the unit circuit 34 b is off and therefore discharging of thepiezoelectric element 40 is stopped.

However, in a case where the control signal Vin falls to less than thevoltage V_(H)/6, then the voltage Vout also tracks the control signalVin and therefore reaches less than the voltage V_(H)/6 as well, and atransition is made from the second state to the first state.

FIG. 11 is a drawing illustrating the operation of when thepiezoelectric element 40 is discharged when the first state is ineffect.

In the first state, the level shifter 36 a is in the enable state. Whenthe voltage of the control signal Vin is lower than the voltage Vout inthis state, then a current corresponding to the voltage between base andemitter flows through the transistor 342 of the unit circuit 34 a.

At this time, the transistor 341 of the unit circuit 34 a is off.

At this time, the electrical current flows in a path that goes from thepiezoelectric element 40→the transistor 342 (of the unit circuit 34a)→the ground G, as illustrated by the arrow in FIG. 11, thusdischarging the charge from the piezoelectric element 40.

The description herein is of the unit circuits 34 a, 34 b by way ofexample, divided between during charging and during discharging, but theoperation is substantially similar for the unit circuits 34 c to 34 f aswell, except for the fact that the transistors 341, 342 controlling thecurrent are different.

That is to say,

the power source wiring 512 supplies the current (charge) duringcharging in the second state, and recovers the current (charge) duringdischarging in the third state,

the power source wiring 513 supplies the current (charge) duringcharging in the third state, and recovers the current (charge) duringdischarging in the fourth state,

the power source wiring 514 supplies the current (charge) duringcharging in the fourth state, and recovers the current (charge) duringdischarging in the fifth state,

the power source wiring 515 supplies the current (charge) duringcharging in the fifth state, and recovers the current (charge) duringdischarging in the sixth state, and

the power source wiring 516 supplies the current (charge) duringcharging in the sixth state.

The recovered charge is redistributed for reuse by the auxiliary powersource section 50.

In the charge path and discharge path in each of the state, there is acommon path from the one end of the piezoelectric element 40 to theconnection points between emitter terminals in the transistors 341, 342.

Typically, the energy P that is stored in a capacitive load isrepresented byP=(C·E ²)/2

where C is the capacitance of a capacitive load such as thepiezoelectric element 40, and E is the voltage amplitude.

The piezoelectric element 40 works by being deformed by the energy P,but the amount of working for discharging the ink is 1% or less inrelation to the energy P. As such, the piezoelectric element 40 can beregarded as a simple capacitance. When a capacitance C is charged at aconstant power supply, energy equivalent to (C·E²)/2 is consumed by thecharge circuit. During discharging, too, an equivalent energy isconsumed by the discharge circuit.

Advantage of Driver

In the first embodiment, when the piezoelectric element 40 is chargedfrom voltage zero to the voltage V_(H), then charging takes placethrough six stages of:

from voltage zero to the voltage V_(H)/6,

from the voltage V_(H)/6 to the voltage 2V_(H)/6,

from the voltage 2V_(H)/6 to the voltage 3V_(H)/6,

from the voltage 3V_(H)/6 to the voltage 4V_(H)/6,

from the voltage 4V_(H)/6 to the voltage 5V_(H)/6, and

from the voltage 5V_(H)/6 to the voltage V_(H).

For this reason, in the first embodiment, the loss during charging ismerely an amount corresponding to the surface area of the region thathas hatching in FIG. 12A. More specifically, in the first embodiment,the loss during charging in the piezoelectric element 40 is merely6/36=(16.7%), compared to the linear amplification for charging fromvoltage zero to the voltage V_(H) in a single burst.

In turn, because discharging is also stepwise in the first embodiment,the loss during discharging is likewise merely 6/36 (=16.7%), comparedto the linear format for discharging from the voltage V_(H) to voltagezero in one burst, as illustrated with the amount equivalent to thesurface area of the region that has hatching in FIG. 12B.

The first embodiment also enables a further reduction of powerconsumption because of the redistribution and reuse of charge recoveredby the auxiliary power source section 50 (described below), excludingcases of discharging from the voltage V_(H)/6 to voltage zero, out ofthe charge recorded as a loss during discharging.

With the configuration of patent document 1 (a “comparative example”),in which one system of control signals shared across a plurality ofpiezoelectric elements are selected individually by a switch of everynozzle and supplied directly to the piezoelectric elements, it isnecessary to fully ensure the amount of current on the paths of thecontrol signals in order for control signals of the proper waveform tobe supplied to each of the piezoelectric elements even in a case wherethe control signals are supplied at the same time to a large number ofpiezoelectric elements. As such, each of the wirings that transmit thecontrol signals and each of the switches that select the control signalsis required to have ample withstand voltage performance and amplewithstand current performance, and a problem arises in that it isdifficult to reduce the scale of circuitry. In the first embodiment,because the above-described configurations and operations allow thedrivers 30, installed for every piezoelectric element 40, to generatethe voltage Vout from the control signal Vin and supply same to thepiezoelectric elements 40, the amount of current on the paths of thecontrol signals COM (COMA, COMB) is considerably reduced in comparisonto the comparative example. As such, the withstand voltage performanceand withstand current performance required for the wirings of the FFC 70that transmits the control signals COM and each of the switches of theselection section 230 are reduced in comparison to the comparativeexample. That is to say, according to the first embodiment, it ispossible to realize a reduction in the scale of circuitry. Anotheradvantage lies in the fact that heat generation by the selection section230 can be avoided, because each of the switches 232 of the selectionsection 230 does not consume power.

Class D amplification has a higher energy efficiency compared to linearamplification. This is due in part to the fact that that an activeelement of an output stage operates at a saturated state and consumessubstantially no power, the fact that the exchange of magnetic energycreated by an inductor L constituting a low-pass filter and energycreated by a capacitance C prevent, during charging, the occurrence ofsuch loss as with linear amplification, and the fact that the electricalcurrent is regenerated to the power source with current switching duringdischarging.

However, actual class D amplification does have problems, among whichthe fact that the resistance of the active element of the output stageis not zero, even in the saturated state, the fact that there is leakageof the magnetic field, the fact that the resistance component of theinductor L causes loss to occur, and the fact that in some instances theinductor L is saturated during modulation.

Class D amplification also has problems in that the waveform quality ispoor and EMI countermeasures are necessary. Though waveform quality canbe improved by adding a dummy capacitance or filter, the increaseentails a commensurate increase in power consumption and rise in costs.EMI derives from the fundamental problem of switching in class Damplification. That is to say, when a switch is made, not only does thecurrent that flows during an on-time reach up to about a factor ofseveral times or several tens of times that of linear amplification, butalso the amount of magnetic field emitted in association therewithincreases as well. Counteracting EMI requires adding a filter and thelike, and entails higher costs.

The drivers 30 of the print apparatus as in the first embodiment do notsuffer the problems of poor waveform quality and the need to counteractEMI, because the transistors 341, 342, which are equivalent to an outputstage, do not engage in such switching as in class D amplification, andalso because inductors L are not used.

Also, the first embodiment involves an operation where the voltage Vouttracks the voltage of the control signals Vin, and therefore finevoltage control is possible with respect to the piezoelectric elements40. That is to say, the start voltage and end voltage of the voltageVout applied to the piezoelectric elements 40 are unrelated to thevoltages V_(H)/6, 2V_(H)/6, 3V_(H)/6, 4V_(H)/6, and 5V_(H)/6 used fordriving.

Auxiliary Power Source Section

FIG. 13 is a drawing illustrating one example of the configuration ofthe auxiliary power source section 50.

As illustrated in FIG. 13, the auxiliary power source section 50 has aconfiguration comprising: switches Sw1d, Sw1u, Sw2d, Sw2u, Sw3d, Sw3u,Sw4d, Sw4u, Sw5d, and Sw5u; and capacitive elements C12, C23, C34, C45,C56, C1, C2, C3, C4, C5, and C6.

Of these, the switches are all single-pole double-throw, and a sharedterminal is connected to a terminal a or b in conformity with controlsignals A/B. When described in a simplified manner, the control signalsA/B are pulse signals for which, for example, the duty ratio is about50%, and the frequency thereof is set to, for example, a factor of about20 in relation to the frequency of the control signals COM. The controlsignals A/B of such description may be generated by an internaloscillator (not shown) in the auxiliary power source section 50, or maybe supplied from the control unit 10 via the FFC 70.

The capacitive elements C12, C23, C34, C45, C56, in turn are for chargetransfer, and the capacitive elements C1, C2, C3, C4, C5 are for backup.The capacitive element C6 is for supplying the power source voltageV_(H).

The switches are in fact configured by combining transistors in asemiconductor integrated circuit, and the capacitive elements aremounted externally with respect to this semiconductor integratedcircuit. Preferably, the semiconductor integrated circuit also has theconfiguration formed with respect to the plurality of drivers 30described above.

Next, the power source wiring 516 that supplies the voltage V_(H) in theauxiliary power source section 50 is connected to one end of thecapacitive element C6 and to a terminal a of the switch Sw5u. A sharedterminal of the switch Sw5u is connected to one end of the capacitiveelement C56, and the other end of the capacitive element C56 isconnected to a shared terminal of the switch Sw5d. The terminal a of theswitch Sw5d is connected to one end of the capacitive element C5 and tothe terminal a of the switch Sw4u. The shared terminal of the switchSw4u is connected to one end of the capacitive element C45, and theother end of the capacitive element C45 is connected to the sharedterminal of the switch Sw4d. The terminal a of the switch Sw4d isconnected to one end of the capacitive element C4 and to the terminal aof the switch Sw3u. The shared terminal of the switch Sw3u is connectedto one end of the capacitive element C34, and the other end of thecapacitive element C34 is connected to the shared terminal of the switchSw3d. The terminal a of the switch Sw3d is connected to one end of thecapacitive element C3 and to the terminal a of the switch Sw2u. Theshared terminal of the switch Sw2u is connected to one end of thecapacitive element C23, and the other end of the capacitive element C23is connected to the shared terminal of the switch Sw2d. The terminal aof the switch Sw2d is connected to one end of the capacitive element C2and to the terminal a of the switch Sw1u. The shared terminal of theswitch Sw1u is connected to one end of the capacitive element C12, andthe other end of the capacitive element C12 is connected to the sharedterminal of the switch Sw1d. The terminal a of the switch Sw1d isconnected to one end of the capacitive element C1.

One end of the capacitive element C5 is connected to the power sourcewiring 515. Similarly, one end of the capacitive elements C4, C3, C2, C1is connected to the power source wirings 514, 513, 512, 511,respectively.

Each of the terminals b of the switches Sw5u, Sw4u, Sw3u, Sw2u, Sw1u isconnected to one end of the capacitive element C1 along with theterminal a of the switch Sw1d. Each of the other ends of the capacitiveelements C6, C5, C4, C3, C2, C1 and each of the terminals b of theswitches Sw5d, Sw4d, Sw3d, Sw2d, Sw1d are grounded alike to the groundG.

FIGS. 14A and 14B are drawings illustrating a state of connection of theswitches in the auxiliary power source section 50.

Each of the switches takes one of two states, a state (state A) wherethe shared terminal is connected to the terminal a or a state (state B)where the shared terminal is connected to the terminal b, depending onthe control signals A/B. FIGS. 14A and 14B provide a simplifiedillustration, with equivalent circuitry, of the connections in the stateA and the connections in the state B, respectively, in the auxiliarypower source section 50.

In the state A, the capacitive elements C56, C45, C34, C23, C12, C1 areconnected in series, from the voltage V_(H) until the ground G. In thestate B, the one ends of the capacitive elements C56, C45, C34, C23,C12, C1 are connected to one another, and therefore the capacitiveelements are connected in parallel, and the holding voltage isequalized.

As such, when the states A, B are alternately repeated, then the voltageV_(H)/6, which was equalized during the state B, is increased by afactor of one to five by the series connection of the state A andrespectively held in the capacitive elements C1 to C5; the holdingvoltage of this time is supplied to the drivers 30 via the power sourcewirings 511 to 515.

Herein, when the piezoelectric elements 40 are charged by the drivers30, a decrease in the holding voltages does appear among the capacitiveelements C1 to C5. The capacitive elements for which the holding voltagehas dropped are resupplied with charge from the power source by theseries connection of the state A, along with equalization withredistribution by the parallel connection of the state B, and thereforea balance is struck so as to stay at the voltages V_(H)/6, 2V_(H)/6,3V_(H)/6, 4V_(H)/6, 5V_(H)/6 when viewed in terms of the auxiliary powersource section 50 overall.

In turn, when the piezoelectric elements 40 are discharged by thedrivers 30, a rise in the holding voltage does appear among thecapacitive elements C1 to C5, but the charge is sent out by the seriesconnection of the state A, along with equalization with redistributionby the parallel connection of the state B, and therefore a balance isstruck so as to stay at the voltages V_(H)/6, 2V_(H)/6, 3V_(H)/6,4V_(H)/6, 5V_(H)/6 when viewed in terms of the auxiliary power sourcesection 50 overall. When the charge that is sent out cannot be absorbedby the capacitive elements C56, C45, C34, C23, C12, C1 and remains inexcess, the excess charge is absorbed by the capacitive element C6,i.e., is regenerated to the power supply system. For this reason, whenthere is any other load beyond the piezoelectric elements 40, the chargeis used to drive this load. When there is no other load, the charge isabsorbed by the other capacitive elements, including the capacitiveelement C6, and therefore the power source voltage V_(H) rises, i.e.,rippling occurs, but increasing the capacitance of the couplingcapacitors, including the capacitive element C6, makes it possible toavoid this in practical usage. As shall be understood from the abovedescription, the auxiliary power source section 50 (capacitive elementsC1, C2, C3, C4, C5) functions as an element (charge supply source) forsupplying a charge to each of the drivers 30 (each of the piezoelectricelements 40).

With the auxiliary power source section 50, when the piezoelectricelements 40 are being discharged by the drivers 30, the holding voltageof any of the capacitive elements C1 to C6 corresponding to the powersource wiring being used for this discharging may temporarily rise, butrepeating between the states A and B strikes a balance so as to hold amultiplication voltage of a factor of one to six of the voltage V_(H)/6.Similarly, when the piezoelectric elements 40 are being charged by thedrivers 30, the holding voltage of any of the capacitive elements C1 toC6 corresponding to the power source wiring being used for this chargingmay temporarily lower, but repeating between the states A and B strikesa balance so as to hold a multiplication voltage of a factor of one tosix of the voltage V_(H)/6.

As will be understood by viewing the voltage waveform of the controlsignals COM in FIG. 4, the voltage rise for drawing in the ink and thevoltage drop for discharging the ink are a set, and this set is repeatedin the print operation. For this reason, with the auxiliary power sourcesection 50, the charge that is recovered by the discharging of thepiezoelectric element 40 is used in charging in the next and subsequentrounds.

As such, in the first embodiment, when the print apparatus 100A isviewed as a whole, the recovery and reuse of the charge discharged fromthe piezoelectric elements 40 and the stepwise charging and dischargingin the drivers 30 make it possible to keep power consumption low.

In the auxiliary power source section 50, when the shared terminals ofeach of the switches are switched from connection to one of theterminals a, b to the other, should there be a property variance in aplurality of (in FIG. 13, ten) switches, then in some instances therecould be a state where the switching is not done in unison, resulting ina short-circuiting of both ends of the capacitor elements. For example,when the terminals a are connected to the shared terminal at theswitches Sw1u, Sw1d, Sw2d during switching, should there occur a statewhere the terminal b is connected to the shared terminal at the switchSw2u, then both ends of the series connection between the capacitiveelements C12, C23 would end up short-circuiting.

For this reason, the configuration is preferably such that duringswitching of the switches, the occurrence of such short-circuiting isminimized through a neutral state in which there is temporarily noconnection to the terminals a, b.

Second Embodiment

FIG. 15 is a block diagram of a print apparatus 100B as in a secondembodiment. As illustrated in FIG. 15, the print apparatus 100B of thesecond embodiment is a configuration in which the print data generationsection 120 and control signal supply section 140 in the control unit 10of the print apparatus 100A of the first embodiment are replaced with acontrol section 160, and the head control section 220 and the selectionsection 230 of the print head 20 are replaced with a signal generationsection 280. In each of the embodiments illustratively exemplifiedbelow, the reference numerals to which reference has been made in thedescription of the first embodiment shall be reappropriated for thoseelements for which the actions and functions are similar to those of thefirst embodiment, and more detailed respective descriptions thereof areomitted as appropriate.

The signal generation section 280 of FIG. 15 is an element for supplyingthe control signal Vin to each of the drivers 30 of the element drivesection 240, and is equipped with a plurality (the same number as thenumber of the piezoelectric elements 40) of control signal generationsections 282 corresponding to the different piezoelectric elements 40.That is to say, the control signal supply sections 282 are in aone-to-one correspondence with the sets of the drivers 30 and thepiezoelectric elements 40. Each of the control signal supply sections282 of the second embodiment is an element for generating the controlsignal Vin and supplying same to the driver 30 of the subsequent stage,and is configured so as to comprise a waveform generation section 284and a D/A converter 286. The waveform generation section 284 generatesthe digital control signal dCOM, similarly with respect to the waveformgeneration section 144 of the first embodiment. The D/A converter 286converts the control signal dCOM generated by the waveform generationsection 284 into the analog control signal Vin, and supplies same to thedriver 30, similarly with respect to the D/A converter 145 of the firstembodiment. That is to say, in the first embodiment, the control signalCOM shared across the plurality of piezoelectric elements 40 isdistributed to each of the plurality of drivers 30 by the selectionsection 230, whereas in the second embodiment, the control signal Vin isgenerated mutually independently for every piezoelectric element 40 byeach of the control signal supply sections 282 and then supplied to eachof the drivers 30.

The control section 160 of the control unit 10 designates the controlsignal Vin that should be generated by each of the control signal supplysections 282, sequentially for each of the plurality of control signalsupply sections 282, in accordance with the image data (print data DP).More specifically, the control section 160 designates the control signalVin for each of the control signal supply sections 282 in every printcycle Ta, so that ink droplets of the amount of discharge correspondingto the image data is discharged by each of the piezoelectric elements 40from the nozzles. Because the control signal Vin is individuallygenerated by each of the control signal supply sections 282 inaccordance with the designation coming from the control section 160, thecontrol signals Vin generated by each of the control signal supplysections 282 can have different waveforms or positions (phases) on thetime axis. That is to say, the amount of ink droplets discharged by thepiezoelectric elements 40 (the diameter of the dots formed on therecording medium with the ink droplets) or the discharge timing (thelanding positions of the ink droplets on the recording medium) areadjusted individually for every piezoelectric element 40.

In the second embodiment, as well, the drivers 30 installed for everypiezoelectric element 40 generate the voltage Vout from the controlsignal Vin and supply same to the piezoelectric elements 40, andtherefore, similarly with respect to the first embodiment, an advantagearises in that the withstand voltage performance and withstand currentperformance required for each of the wirings and each of the circuitscan be reduced in comparison to the comparative example. Additionally,in the second embodiment, each of the control signal supply sections 282generates the control signal Vin individually for every piezoelectricelement 40. As such, an advantage arises in that the waveform orposition of the control signal Vin can be adjusted for everypiezoelectric element 40 in accordance with, for example, the propertiesof each of the discharge sections 400 (for example, the conversionefficiency of the piezoelectric elements 40) makes it possible to reducethe impact of differences in the properties of each of the piezoelectricelements 40.

Application/Modification Examples

The present invention is not limited by the embodiment described above,but rather, a variety of applications and modifications, such as shallbe described below by way of example, are possible. One or a pluralityof arbitrarily selected embodiments of application or modificationdescribed below can also be combined as appropriate.

Negative Feedback Control

FIG. 16 is a drawing illustrating one example of the configuration ofthe driver 30 as in a (first) example of application of the embodiment.As illustrated in FIG. 16, this example of application takes aconfiguration in which the voltage Vout of one end of the piezoelectricelement 40 is negatively fed back to the input end (−) of theoperational amplifier 32. With this configuration, when a differenceexists between the voltage of the control signal Vout and the voltageVout, then the transistors 341, 342 are controlled in a direction thateliminates this difference. For this reason, even in a case where theresponse properties of the level shifters 36 a to 36 f or thetransistors 341, 342 are poor, the voltage Vout can be made torelatively quickly and very precisely track the control signal Vin.

Regarding the amount of negative feedback, the configuration preferablyallows for property setting in accordance with the properties of thelevel shifters 36 a to 36 f and the transistors 341, 342. For example,in the depicted example, the operational amplifier 32 is configured tooutput a voltage obtained by subtracting the voltage Vout from thevoltage of the control signal Vin, but the configuration may be suchthat this subtracted voltage is multiplied by an appropriate factor andthen supplied to the level shifters 36 a to 36 f.

FIG. 17 is a drawing illustrating one example of a configuration of thedriver 30 as in another (second) example of application of theembodiment. In the driver 30 described in FIG. 5, the transistors 341,342 of the unit circuits 34 a to 34 f were of a bipolar type, but in the(second) example of application illustrated in FIG. 17, the transistors341, 342 are made to be Metal-Oxide-Semiconductor Field-EffectTransistors (MOSFETs) 351, 352 of a P- or N-channel type, respectively.

In the case where the MOSFETs 351, 352 are used, it suffices to providediodes for preventing reverse current between each of the drainterminals and the one end of the piezoelectric element 40. Also,regarding the level shifters 36 a to 36 f in the case where the MOSFETs351, 352 are used, the configuration is such that when the enable stateis in effect, the voltage of the control signal Vin is shifted by anamount equivalent to a threshold voltage, as the predetermined value, inthe minus direction and then the shifted voltage is supplied to a gateterminal of the MOSFET 351 of the P-channel type, and in turn thevoltage of the control signal Vin is shifted by an amount equivalent toa threshold voltage, as the predetermined value, in the plus directionand then the shifted voltage is supplied to a gate terminal of theMOSFET 352 of the N-channel type.

A configuration, such as is illustrated in FIG. 16, in which the voltageVout is negatively fed back may also be applied in the case where theMOSFETs 351, 352 are used.

Driven Objects

The foregoing embodiments describe the piezoelectric elements 40 by wayof example as the driven objects of the drivers 30. The presentinvention is not limited to the piezoelectric elements 40 as the drivenobjects, and may be applied to any and all loads that have a capacitivecomponent, such as, for example, an ultrasonic motor, a touch panel, aflat speaker, or a liquid crystal or other kind of display.

Number of Stages of Unit Circuits

The embodiment had a configuration in which six stages of unit circuits34 a to 34 f are provided in ascending order of voltage, so as tocorrespond to two mutually adjacent voltages out of the seven types ofvoltages, but in the present invention, the number of stages of unitcircuits is not limited thereto, and need only be two stages or more.The voltages, too, need not necessarily be evenly spaced.

Comparators

The embodiment had a configuration in which, for example, the firststate is detected as being in effect when the determination result ofthe comparator 38 a is false (when the output signal is the L level) andthe second state is detected as being in effect when the determinationresult of the comparator 38 a is true (the output level is the H level)and the determination result of the comparator 38 b is false. That is tosay, the configuration for detecting the first state and second state isa configuration of partial overlap, not separation from one another, anda configuration in which the first state to sixth state are detectedwith the entirety of the comparators 38 a to 38 e. There is nolimitation thereto, and the configuration may also be one where each ofthe states is detected individually.

Level Shifters in Disable State

The embodiment has a configuration in which the level shifters 36 a to36 f, which in the disable state, supply voltage zero to the base (gate)terminals of the transistors 341 (351) and supply the voltage V_(H) tothe base (gate) terminals of the transistors 342 (352), but there is nolimitation thereto, provided that the transistors 341, 342 can be turnedoff. For example, the configuration may be one where the level shifters36 a to 36 f, when in the disable state, supply an off signal, obtainedby shifting the voltage of the control signal Vin in the plus direction,to the base (gate) terminals of the transistors 341 (351) and supply anoff signal, obtained by shifting the voltage of the control signal Vinin the minus direction, to the base (gate) terminals of the transistors342 (351).

According to this configuration, the breakdown voltage of thetransistors 341 (351), 342 (352) is lower, and therefore it is possibleto reduce the transistor size of when transistors are being formed onthe semiconductor substrate.

General Interpretation of Terms

In understanding the scope of the present invention, the term“comprising” and its derivatives, as used herein, are intended to beopen ended terms that specify the presence of the stated features,elements, components, groups, integers, and/or steps, but do not excludethe presence of other unstated features, elements, components, groups,integers and/or steps. The foregoing also applies to words havingsimilar meanings such as the terms, “including”, “having” and theirderivatives. Also, the terms “part,” “section,” “portion,” “member” or“element” when used in the singular can have the dual meaning of asingle part or a plurality of parts. Finally, terms of degree such as“substantially”, “about” and “approximately” as used herein mean areasonable amount of deviation of the modified term such that the endresult is not significantly changed. For example, these terms can beconstrued as including a deviation of at least ±5% of the modified termif this deviation would not negate the meaning of the word it modifies.

While only selected embodiments have been chosen to illustrate thepresent invention, it will be apparent to those skilled in the art fromthis disclosure that various changes and modifications can be madeherein without departing from the scope of the invention as defined inthe appended claims. Furthermore, the foregoing descriptions of theembodiments according to the present invention are provided forillustration only, and not for the purpose of limiting the invention asdefined by the appended claims and their equivalents.

What is claimed is:
 1. A liquid discharge apparatus comprising: a firstdischarge section and a second discharge section each having a nozzleconfigured and arranged to discharge a liquid, a pressure chamber incommunication with the nozzle, and a piezoelectric element provided forthe pressure chamber and configured and arranged to cause the liquid tobe discharged from the nozzle by charging and discharging in accordancewith a drive signal; a first connection path selection sectionconfigured to selectively supply a plurality of voltages to the firstdischarge section, the first connection path selection section beingarranged so as to correspond to the first discharge section; a secondconnection path selection section configured to selectively supply aplurality of voltages to the second discharge section, the secondconnection path selection section being arranged so as to correspond tothe second discharge section; and a voltage generation sectionconfigured to generate and supply the voltages shared by the firstconnection path selection section and the second connection pathselection section.
 2. The liquid discharge apparatus of claim 1, furthercomprising a control signal supply section configured to supply acontrol signal, a first switch configured and arranged to controlsupply/shutting off of the control signal to the first connection pathselection section, and a second switch configured and arranged tocontrol supply/shutting off of the control signal to the secondconnection path selection section, wherein the first connection pathselection section is configured to selectively supply the voltages tothe first discharge section in accordance with the control signalsupplied from the first switch, and the second connection path selectionsection is configured to selectively supply the voltages to the seconddischarge section in accordance with the control signal supplied fromthe second switch.
 3. The liquid discharge apparatus of claim 2, whereineach of the first connection path selection section and the secondconnection path selection section is configured and arranged to controla charge with which the piezoelectric element is charged or a chargedischarged from the piezoelectric element, at a voltage obtained when avoltage found by subtracting a voltage held by the piezoelectric elementfrom the voltage of the control signal is multiplied by a predeterminednumber.
 4. The liquid discharge apparatus of claim 1, further comprisinga first control signal supply section configured to generate a controlsignal and selectively supply the control signal to the first connectionpath selection section, the first control signal supply section beingarranged so as to correspond to the first connection path selectionsection, and a second control signal supply section configured togenerate a control signal and selectively supply the control signal tothe second connection path selection section, the second control signalsupply section being arranged so as to correspond to the secondconnection path selection section, wherein the first connection pathselection section is configured to selectively supply the voltages tothe first discharge section in accordance with the control signalsupplied from the first control signal supply section, and the secondconnection path selection section is configured to selectively supplythe voltages to the second discharge section in accordance with thecontrol signal supplied from the second control signal supply section.5. The liquid discharge apparatus of claim 1, further comprising a firstsignal path through which a first voltage is applied by the voltagegeneration section, and a second signal path through which a secondvoltage higher than the first voltage is applied by the voltagegeneration section, wherein the first connection path selection sectionelectrically connects the first discharge section and the voltagegeneration section by the first signal path or the second signal path inaccordance with a voltage of a control signal and a holding voltage ofthe piezoelectric element, and the second connection path selectionsection electrically connects the second discharge section and thevoltage generation section by the first signal path or the second signalpath in accordance with the voltage of the control signal and theholding voltage of the piezoelectric element.
 6. The liquid dischargeapparatus of claim 5, further comprising a detection section configuredand arranged to detect whether or not the holding voltage of thepiezoelectric element is less than the first voltage, or whether or notthe holding voltage of the piezoelectric is between the first voltageand less than the second voltage.
 7. The liquid discharge apparatus ofclaim 5, wherein each of the first connection path selection section andthe second connection path selection section is configured and arrangedto control a charge with which the piezoelectric element is charged viathe first signal path in conformity with the voltage of the controlsignal at less than the first voltage, and to control a chargedischarged from the piezoelectric element via the first signal path or acharge with which the piezoelectric element is charged via the secondsignal path in accordance with the voltage of the control signal atbetween the first voltage and less than the second voltage.
 8. Theliquid discharge apparatus of claim 5, wherein each of the firstconnection path selection section and the second connection pathselection section includes a first transistor, a second transistor, anda third transistor, wherein at less than the first voltage, the firsttransistor controls a charge with which the piezoelectric element ischarged via the first signal path in accordance with a voltage obtainedwhen the voltage of the control signal is shifted by a predeterminedvalue to a low side, and at between the first voltage and less than thesecond voltage, the second transistor controls a charge discharged fromthe piezoelectric element via the first signal path in accordance with avoltage obtained when the voltage of the control signal is shifted bythe predetermined value to a high side, and the third transistorcontrols a charge with which the piezoelectric element is charged viathe second signal path in accordance with a voltage obtained when thevoltage of the control signal is shifted by the predetermined value tothe low side.
 9. The liquid discharge apparatus of claim 8, wherein thefirst transistor is off at not less than the first voltage, and thesecond transistor and the third transistor are off at not between thefirst voltage and less than the second voltage.